The present invention relates to a system (method and apparatus) for determining the concentration of certain constituents of a body fluid, such as urine or blood.
Recently, test carriers, for example in the form of test strips or in the form of flat, approximately square platelets, have been used increasingly for the analysis of body fluids, especially of urine and blood. Analytical determinations, especially for medical purposes, can be carried out particularly easily with these test carriers. The test carriers are first of all brought into contact with the sample. When examining urine, this is generally done by dipping a strip-shaped test carrier into the urine. For examining blood, a drop of blood is usually applied on the test field of the test carrier and, after saturating the test field, is wiped or washed off. In each case, the test field, which represents the part of the test carrier that is crucial for the analytical determination, contains reagents that react with the components of the body fluid that has been applied.
To evaluate the reaction, the test carrier is placed in appropriate evaluating equipment, in which a physical quantity, which serves as a measure of the concentration of a particular component of the body fluid, is measured at a specified time after the sample is applied. To analyze body fluids, a reaction is predominantly used that produces a color change characteristic of the analysis to be carried out. In this case, the diffuse reflectance of the test field at a particular wavelength is usually determined as the physical quantity measured. Such test carriers can thus be evaluated photometrically. In a different, known type of test carrier an electrochemical reaction is utilized to analyze the body fluid. In this case, a voltage or an amperage is determined as the physical quantity characteristic of the analysis.
The test carriers are usually suitable specifically for a particular analysis: that is, for determining the concentration of a specific component of a body fluid - a so-called "parameter". Thus, for each parameter it is necessary to provide a particular test carrier type. To evaluate the test carriers, equipment is used which is either adapted specifically to one such carrier type (single parameter equipment), or which can measure several different test carriers (multiparameter equipment).
The test carrier and the associated evaluating equipment, which together form a system, must satisfy very high accuracy requirements. Usually, a large number of test carriers is produced together under constant conditions. For example, for photometrically evaluable tests, a particular carrier matrix for the test fields and a single preparation of reagents is used for one manufacturing batch. The test carriers of such a manufacturing batch are therefore practically identical in their properties. On the other hand, test carriers from different manufacturing batches deviate from one another with respect to their evaluation curves; for example, in the relationship between the diffuse reflectance of the test field and the concentration of the sought-after parameter which is to be determined by the equipment. These deviations are so large, that the high requirements set in medicine for quantitative determinations cannot be fulfilled if the differences between the different manufacturing batches are disregarded.
In principle, the desired accuracy could be attained by calibrating with standard solutions before each use of the test carrier. This, however, makes it more difficult and time consuming to utilize the analytical system.
It has therefore already been previously proposed to transmit, in a suitable manner, that information concerning the batch -specific evaluation curve of the respective test carrier batch to the evaluating equipment. For example, as is described in U.S. Pat. No. 4,592,893, the individual test carriers may be provided with a bar code, which contains information relating to the batch-specific evaluation curve. The associated evaluating equipment contains a bar-code reader to pick up this information. U.S. Pat. No. 4,578,716 describes strip-shaped test carriers which have a magnetic layer that is also suitable for the storage and retrieval of information. This information is written into the magnetic layer by the manufacturer of the test carrier and sensed by the evaluating equipment with an appropriate magnetic read head.
These two known transmitting techniques are particularly convenient to handle because the necessary information is in each case communicated automatically to the equipment without any intervention whatsoever by the user. This advantage is, however, accompanied by considerable cost. In manufacturing the test carrier, the information must be transferred to each individual test carrier and special test carriers, coordinated with the respective instrument type, must be produced. In the evaluating instrument, there must be an appropriate reading device which increases the cost of the instrument appreciably.
For simpler equipment, especially for determining blood glucose values for diabetics, it is therefore largely customary to disregard the batch-specific variations of the test carriers. This, however, leads to medically intolerable inaccuracies.
In a different, known instrument for determining blood glucose, the batch-specific evaluation curve, in the form of a bar code, is included separately from the test carriers in the test-carrier packages. The costs of manufacturing the test carrier are thus reduced. However, in this case, the equipment must also have a code reader and thus becomes appreciably more expensive.